Long submarine telegraph cable for operation at high speed



June l 1926. 1,586,874

o. E. BUCKLEY LONG SUBMARINE TELEGRAPHv CABLE FOR OPERATION AT HIGHSPEED Filed August 16, 1921 "l'loade'd telegraph'conductor over which.sig'

limited byv certain factors, notably elec?. trostatic capacity,resistance, transmitting Patented `lune 1 1.1926,-

- TEIC COMPANY, INCORPORATED, or NEW-vonk, N. Y.,'A CORPORATION or NEW 1LONG "sir-mira:initia- 'PELEGRAPH CABLE. Pon OPEEA'T'IONAT HIGH SPEED.

Application"alea august 16,31921; fs'eiiaiNo. 492,7a5.

I This'inventionjrelates to the'artvof telegraphy, and particularly 'toan .-in'ductively loaded .conductor -for `long submarine -telegraphcables. 1' 5 An obj-ect of thisinvention is to provide a Anals "may betransmitted at far greater speeds than have heretofore been possible.

Figs. l and 2 are diagrams that Willfbe 0 referred to in discussingtheprinciples of the. invention; Fig. 3 is a section. of a fur. nace-forannealingthe loaded conductor;-

and Fig.. 4 is acircuit diagram for a telegraph .cable embodying theinvention. v

commonly been of one type,`a single copper z conductor surrounded by a'layer of insulating material, usually gutta percha, and provided with aprotective sheath; With a cable of this type, the maximum speed oftransmission 1Which"inay beattained is I -voltage andinterferingdisturbances.`

" decreasing the resistance or capacity or both, but the factors ofcost' Vandmechanical "difficulties have heretofore'been, considered tovhave set -a practical limit of conductor gutta percha about .45 iilch;

In common practice, it is 4 considered, de-

sirable -to limit the sending lvoltageto volts; higher voltagesinvolvesome risk of4v among these components. W'ithin recent ,years means havebeen developed for corbreaking down' ythe insulation, 'and :this isconsidered the limit for safety.

ocean cable, Without any battery electromotive force applied thereto,maygliave fre-i quent slight currents'set vupby practically unknov'vjnelectrom'otive forces. Similar curi. Y rents are also encountered-inlandtelegraphy, 'and 'somewhat similar in'characteris fthel -socalled lstatic"fwhich limits operations inradio -telegraphy and telephony. In

10 micro-amperes in order that it may be easily detected in .comparisonWith ythe interferingdisturbance's that have been menttioned.. j .y Inthe clase ofv a relatively large cable of length 2000 nauts, suitablefor transoceanic operation, having a conductor of 660 pounds Longsubmarine telegraph cables/have- Some gain inzspeed might be securedbydiameter about .2 Ainch and diameterl over' A longordinary Cases. inthe pa'stfit'has been consideredthat fin long submarine telegraph..

lines, the receivedfcurrent should be about of. copper [per naut,-l andinsulated. with.v 400 pounds of gutta perch'a per naut, thefrevquency'is limited by interference to about 10 cycles per second, and if' about1 0 microamperes is to be received 'on' -5 0 volts send# ing, thefrequency must' be even4 less than y10.

-Whatever the system of .signaling employed there` vvill be somelimiting frequency ofv transmitted impulses necessary to be received Adiscretely inorder to make the signa-ls inv telligible, this beingordinarily designated as the signaling frequency. If this speed ofsigna-ling is attempted vto be increased above prevent their accurate.interpretation.

It has long been knownthat, in general, u

the attenuation of signals by transmission lines could. be reducedby theaddition of inductance 1n proper amount. Many proposals have been madeinthe past toim-l ,prove submarine telegraph cable `operation bythe useof added inductance. However,

most of these proposals have had the -pri-v mary objectof reducing'distortion rather than attenuation, since distortion has been thefactor which, until recently, has practically limited the speed ofsignaling.

' It will beunder'stood that distortion'in '.telegraphy results from anunequal? attenuation of the sine Wave components for various'frequencies, and a relative phase shift recting' distortion to.anynecessary degree l tion relative to the .unloaded line for thefrequencies involved insignaling, so thata4 higher signal speed can beemployed Without misinterpretation of the signals due to the normaldisturbance currents.

Two Ways of loading-submarine cables have. been used-for .relativelyshort telephone c'ab1es. -These are coil loading 'by meansof inductancecoils at suitable inter vals in series with the conductor, and con'-tinuous loadingbymeans of alayer of iron Wire Wrapped directly aroundthe conduc tor. In-many cases, suchtelephone cables I have been used forsuperposed direct current telegraphy, but the loading has been ofsubstantial advantage only for the telephone service and for highfrequency carrier telegraph service. In practically no case has any meretelegraph cable been loaded, Whether long or short, and the fact thattelegraphing has been done on loaded cables is only incidental to thecircumstance that they Were intended primarily for telephony and wereloaded for that purpose. f

The longest cable that has been loaded for telephone purposes to thepresent time has a length of about 110 miles. This cable is continuouslyloaded by means of a Wrapping of iron Wire. In a few instances, shorttelephone cables have been laid with elongated loading coils atintervals Within the insulation, but mechanical difliculties present aserious obstacle to this practice.

Aside from attempting to increase the speed of long lines by theaddition of inductance, another proposal that has been considered is tointroduce leaks at points uniformly distributed along the lines. Thiscorrects distortion to a certain extent, but greatly increasesattenuation, so that it is Vnot considered to be an advantageousexpedient on the whole.

Notwithstanding the Well-recognized desideratum of a suitable inductanceloading for a long submarine telegraph conductor, and that no scheme forloading such a conductor, Whether long or short, has ever beendemonstrated to be advantageous, it has now been found that a longtelegraph cable can be continuously loaded in a practical manvner With acomposition of especial characteristics which will be pointed out, sothatit will transmit telegraph signals at speeds many times those whichare possible With the ordinary /non-loaded cable, or indeed with a cab econtinuously loaded yin accoi-dance with the plans hitherto proposed.The important advantage of using this composition lies in the fact thatalthough its l permeability at higher magnetizing forces may be nogreater than that of iron, nevertheless, at the low magnetizing forcesencountered in a telegraph cable, its permeability is much higher thanthat of iron. For one-Way sending in an ocean cable, the receivedcurrent may fall as loW as 10 microamperes, or even lower, whichcorresponds to an exceedingly low magnetizing force. Even at the sendingend, Where the full effect of the 50 volt applied electromotive force isfelt, the current will give a magnetizing force of only .about 0.2electromagnetic unit. Thus, the composition Which is contemplated foruse has its remarkably high permeability Within the range of magnetizingforces corresponding to those associated with signaling currents in along submarine conductor.

the loading material Wrapped around it. v

But the addition of the loading material necessitates more insulatingmaterial and makes a more expensive cable, and it may be that if copperwere addedrin place of the loading material, the received current `Wouldbe even greater than for the loaded conductor. Thus it will be seen thata better basis of comparison is that the conductor and the loadingmaterial combined shall have the same over-all diameter as the unloadedconductor. That is, the loading material should,

be considered as replacing an outer layer of the copper conductor; ifthe loaded conductor does not offer advantage under this condition, itwould be better not to replace the copper with loading material.

Accordingly, the question -of setting up a criterion for the advantageof loading presents itself as folloWs-What are the conditions that Willmake it advantageous to replace a vanishingly thin outer shell of theconductor by loading material? This leaves the quest-ion of the optimumthickness of the loading material to be determined later, but at presentwe are seeking the condition as to Whether the optimum thickness shouldbe zero, or some amount not yet determined, greater than zero.

The problem of telegraphic transmission of signals is fundamentally oneof transients. Howeven in a case Where the speed of signaling is limitedby attenuation and' interference, which is the case with which We areconcerned, the question of maximum speed of signaling can be moreconveniently discussed with reference to what happens to a steadyvalternating current. This results from the fact that for any givensystem and speed of signaling there corresponds a frequency oftransmitted impulses which must be received discretely in order to makethe received signals legible. This frequency is ordinarily designatedthe signaling fre'- quency. If a series of equal impulses alternatelypositive and negative are transmitted at this speed they are receivedapproximately as a sine Wave alternating current, the higher frequencycomponents of the signals having been damped out by the cable. Theattenuation of the series of irnpulses is thus approximately the same asthe attenuation of a steady alternating current of frequency in cyclesper second equal to half the number of impulses per second,

and if the signal is made up of an irregular combination of impulses theattenuation of the signal as a Whole when properly corrected by terminalcircuits, maybe deter- -mined by the attenuation of a steady alternatingcurrent of frequency equal to half that of the highest frequencyimpulses necessary to be received in order to make the y signal legible.

A formula will nonr be derived lshowing the relation that must besatisfied by the permeability and other factors so that the replacementof conductor material by' loading material shall be advantageous.

The attenuation a per unit length for a current of frequency fn' in acontinuously loaded conductor having per unit length the resistance R',capacity K and in ductance L, is given by the Well-known formula on theassumption that the leakance is negligible, Which is an entirely validassumption to be made in this case. Since We are considering the effectof a vanishingly thin outer layer of magnetic material, the value of Lwill be very small and the term 47271/2112 will be so small incomparisonwith R2 that Now, With a constant over-all radius r, We

it may be neglected, thus reducing the .for-

mula to see that when We apply a layer of magnetic material of thicknesst, we not only increase L but we diminish the cross-section of theconductor, and thereby increase R. Hence, to decrease a, We mustincrease the term QvrnL more than we increase the term R. Accordingly,/taking the derivatives of these .terms with respect to t, we must havelf the specific resistance of the conductor material is p, theresistance of the conductor per unit length is given by Since we aredealing with a vanishingly thin layer of loa-ding material, theforegoing equation reduces to d y aR To obtain an expression for 'theinductance due to the layer of loading material,

we introduce first the Well-known formula that which gives theintensity'ofthe magnetizingforce H at the surface of a conductor ofradius 1' carrying current I. Assuming the permeability of the magneticmaterial is a, the flux` density B is given by the formula and the fluxper unit length of the conductor is But by the deinitionof inductanceSubstituting in the critical inequality Written out heretofore,

is the resistance R per unit length of the unloaded conductor, hence theinequality on which We rely as the criterion may be `Written -R #mit Ifthe values of permeability y, frequency n, and resistance R satisfy theforegoing inequality, then We are assured that the replacementof avanishingly thin outer layer of conductive material by a similar layerof magnetic materiall will decrease the attenuation of a currenttherein, but if the that a magnetic material of a certain permeabilitymay be highly advantageous vin connection with telephone frequencies andof no advantage for telegraph frequencies. Since the product a n must belarger than a certain amount, and since the frequency n is relativelyhigh for telephony, the permeability a need not be high, but when 'n islow as for telegraphy, then a must be high to make the product ,a nsuficiently large. This inequalityfalso exhibits the fact that for givenvalues of a and a, a decrease of resistance R may change the situationfrom unfavorable to favorable for the addition of loading material.

Passing now to a specific example under this criterion, considerationwill be given to a representative cable having a resistance of 1.80 ohmsper naut, that being the resistance of the particular copper conductorof 660 pounds per naut heretofore mentioned. Changing to electromagneticunits, and performing the'indicated division by 21T, the inequalityreduces to cable. At such low magnetizing forces, the

permeability of the magnetic circuit when iron is employed as theloading material is only about 150. Hence we see that to satis- -fy theforegoing inequality, fn, must have a value of at least 10 cycles persecond. If n, the signaling frequency, is less than 10 cycles persecond, there will be no improvement in 'attenuation by addingcontinuous loading. On the other hand, althou h the criterion mayapparently be satis ed by increasing n, the fact is that at. higherfrequencies `the attenuation in a cable loaded with iron is so muchgreater that the signals will be unitelligible. The curve in Fig. l,shows how abruptly the received current decreases with increasingfrequency-in an unloaded cable of fairly representative dimensions, butfor somewhat ideal conditions.

In this figure, the ordinance represent the received current inmicro-amperes for an impressed electromotive force of 50 volts, and theabscissae represent the frequency in cycles per second.

Though it may sound paradoxical, loading with iron would be of advantagein such a cable for telephony, but the trouble would be that, at thehigh frequency employed, the

where 8 is an increment depending upon the circumstances, among which isthe fact that we cannot deal in a practical manner with a layer ofloading material of only vanishing thickness.

Another factor which would increase and which contributes to prevent theuse of iron loading for even relatively short cables,

, is the circumstance that as soon as the loading material has asensible thickness, it becomes the seat of eddy currents which increasethe alternating current resistance of the cable as compared with itsdirect current resistance.

Still another factor which -helps to prevent the use of iron loadingeven for relatively short cables is that of the difficulty of balancingfor duplex opera-tion. In order to operate a cable simultaneously inboth directions, it is necessary to provide at each end a balancingnetwork or artificial line having an impedance equal to'that of thecable over the frequency range involved. To attain the speeds of presentcommercial practice over long cables, a very high degree of perfectionof balance between the artiicial line and the cable is required. Abalance accurate to one part in ten thousand is often necessary withordinary non-loaded cables, and the attainment of this degree of balanceis a very difficult matter. However, the problem of balancing acontinuously loaded cable is far more difficult than that of balancing anon-loaded cable, owing to the fact that the. impedance is no longerconstant even for a single frequency, but varies with the amplitude ofthe sending current as a result of the variation of the permeability ofthe loading material corresponding to variation of the magnetic fieldstrength. Moreover, the problem of balance becomes increasingly dithcultat higher speeds.

Of course this difficulty as to balancing a high speed loaded cable, sayof 1,000 miles or over, may be obviated by operating in only onedirection at a time, but in that case, for the continuously loaded cableto offer added asthe loading material, this would inhibit eiicientduplex operation and hence to compare favorably, the cable must have aone-way speed of cycles per second when loaded. This is out of thequestion because, .as previously stated, at the high frequency employed,the received current would be far too small to be appreciable.

In a tape-loaded cable the inductance pei` nant is .Where d is theover-all diameter of the conductor and loading and t is the'thickness ofthe tape.' In this cable, with a copper-.conductor and with the loadingmaterial 781% nickel and 211/2% iron, the resistance perv naut (takingaccount of eddy current losses f a, gives the attenuation in the loadedcable.

In Fig. 2 are shown the results of computati-ons which have been made bymeans of the foregoing formulas, giving the effect of permeability onsignal speed in representative cases. The curves of Fig. 2 show the ythe manner in which the maximum attain able frequency o-f signalinimpulses varies with the permeability of oading material employed.lThreel cases are presented for which the conductordiameters in inchesare respectively 0.150, 0.180-, and 0.200. The capacities of the threecables are each assumed to be 0.4 microfarads'4 per naut. In all ofthese cases, ay length of 2,000 nauts is assumed. This length is fairlycomparable with the length of the trans-atlantic cables thatconnectvEurope and North America, and, therefore, 1s convement as an examplefor comparison. This inventlon 1s not applicable to .short cables of thekind that connect England with the continent, Cuba with the UnitedStates, etc., and 2,000 nauts is` mentioned as a representativelength,not as a limit. p

For the curves ofFig. 2,- a transmitting voltage of 50 volts is assumed,and it is also assumed that the received current is about forces .Withnickel and cobalt 1n thlsrespect, stands chosen was in each case theoptimum thickf ness, that is, the thickness which would give thegreatest received current; in other words, the thickness which wouldgive the least attenuation. These thicknesses in thousandths of an inchare indicated by the numbers in parenthesis noted at correspondingpoints on the diagram. They vary from point to point along each curve.It will be noticed that for low values of permeability all the curvesare substantially horizontal, indicating that the signaling speed isinde pendent of the permeability. This is true .because for low valuesof permeability, the optimum thickness of the loading material is zero,and since the signal speed is accordingly quite independent of the layerof loading material when its thickness is zero, the curves arehorizontal straight lines in the range considered.

These curves take into account the eddy current losses in the magneticmaterial,'cal

culated on the basis of la fixed resistivity but they do not take intoaccount dielectric leak-- ance or the resistance of the return path,

which are quite negligible at low frequencies' but may becomeappreciable at higher frequencies. The effect of including these losseswould be to shorten the ordinates of the curves.

It will be noted that the smaller the diameter of the conductor, thelarger .becomes the required permeability to show any gain as a resultof loading.

In order that the'speed of the loaded cable may be twice that of thecorresponding nonloaded cable, which, as has beenpointed out, will benecessary if duplexing is abandoned, in order to make the loaded cableeven barely worth while, there is required in the case of the conductorof 0.200 inch diameter a magnetic material of permeability about 310.,and for the conductors of diameters 0.180 and 0.150 inches,respectively, the required permeabilities are seen to be about 600 and1,350. Thus it is shown that iron, with a permeabilitygof 150 orthereabouts, would be quite uselessv for loading cables of thesedimensions, but thata material with a permeability several times that ofiron would produce a very great increase in the permissible speed ofsignaling.

Silicon steel exhibits magnetic qualities superior to ordinary iron insome respects, but its employment is limited-by its comparativebrittleness and the difficulty of Working it. The principal possiblerlvals of iron, namely, nickel and cobalt, are far below it inpermeability at the magnetizing involved; in telegraph signaling.

Heuslers alloy of aluminum, manganese and copper. It has been found thata composition of tivo-thirds nickel and one-third cop.- per, when testedat lovv magnetizing forces, gives a permeability higher than that ofiron alone. It will be seen that With the exception of aluminum, allthese metals stand close together in their atomic Weights and atomicnumbers, and in this specification the ive elements, manganese, iron,nickel, cobalt and copper, having the consecutive atomic numers, 25, 26,Q7, 28, 29, will be referred to as belonging to the magnetic group ofelements. A

It has been found that by melting nickel and iron together in properproportions, and by subjecting the composition to suitable heattreatment and mechanical treatment, a magnetic material is producedWhich has a very much greater permeability at loiv magnetizing forcesthan has iron. More particularly, by combining these t\vo elements inproportionof HB1/2% nickel and 2l1/2% iron, and subjecting them toappropriate heat treatment, and other treatment, a material is producedof extraordinarily high permeability7 at low magnetizing forces. Vhenapplied to a conductor in the form of a helical tape with the edgesclose together, it shoivs a virtual permeability of 2,000 or more. Byreference to the curves of Fig. 2, it will be at once seen that forsuchhigh permeability, very great increases in speed are obtainable,whereas iron otlers no advantage when used in the same way.

' Although a permeability of 2,000 or more may be obtained by the use ofthe nickel-iron composition which is herein referred `to as the loadingmaterial, it may not always be desirable to use material of the highestpossible permeability, particularly in the case of cables of less lengthover T,vhich the signaling frequency may be relatively high and forwhich, accordingly, the alternating cui-- rent losses are ofconsiderable consequence. These losses result from causes among Whichare dielectric leakance, eddy currents in the loading material,hysteresis in the loading material, and resistance tothe return currentoutside the cable core. Of these, only eddy current and hysteresis areprimarily dependent upon the loading material. One of the properties ofthe nickel-iron composition, in addition to its high permeability atlowvmagnetizing forces, is its remarkably low hysteresis, and this isone of its incidental advantages. One of the most important of thealternating current losses in the case of the continuously loaded oceantelegraph cable is that due to eddy currents. This factor increases inproportion to the conductivity and the square of the permeability of theloading material and to the square of the frequency. It is also dependcnt upon the dimensions of the tape. In order to reduce the eddy currentlosses for the loaded Conductor, it may be desirable to use a materialof higher specific resist-A ance than the nickel-iron composition Whichl have mentioned specifically, even though this higher resistance isobtained at the expense of lower permeability. Such a material of higherspecific resistance may be obtained by adding chromium in moderateproportion to the nickel-iron composition already mentioned. It is alsoimportant to take into account the eddy current losses in determiningthe thickness of the loading material and to use such a thickness thatthe highest possible frequency will be receivedv With the necessarycurrent amplitude. lt may be advantageous further to reduce the eddyCurrent losses by applying the loading material in the proper thicknessin the form of two or more layers separated by a film of oxide or otherinsulating material.

While 781% and SM1/2% are mentioned as giving the proportion of theingredients, nickel and iron, to be employed in making up the magneticmaterial, it will be understood that the proportion may deviateconsiderably from these figures when nickel and iron are the onlyingredients, and that when there are other ingredients this proportionmay not apply. Up to the present time, When the only ingredients arenickel and iron, it has been found that a proportion about the same ashas been named, gives the greatest permeability for low magnetizingforces. Other ingredients than nickel and iron may b-e employed forvarious purposes, not only to' confer high permeability on the productbut for other objects, such as to increase the specific resistance asshown by the example already mentioned of adding chromium, or tofacilitate mechanical preparationiof. the loading material by making itmore malleable. A composition of nickel iron 34% and chromium 11% hasbeen carefully prepared, heat treated and tested, and found to give apermeability :tar higher than of iron and at the same time to givearesistivity higher than that of iron. and higher than that of thenickel-iron composition in the proportion of 7 5B1/2% nickel and 2l1/2%iron.

In constructing a loaded submarine telegraph conductor in accordanceWith the present invention, a copper conductor is lprovided having arelatively smooth exterior surface. The reason for having the condctorin this form is so that the position of the loading material relativetothe conductor will suffer no change when the cable in Which it isincorporated is submerged and thus sub'ected to rather large pressuresin the dept of the ocean. As is Well known, it. is desirable to employconductors made up of several strands so as to Alend flexibility,thereby providing that a discontinuity of the electrical circuit willnot be so likely to result from a break in the conducto be used. For aconductor of 660 pounds per naut and of length 2,000 nauts, designed tooperate at the maxium practicable speed,

the nickel-iron loading composition should be approximately- 0.006 inchthick and it may be conveniently applied in the form of a tape of thatthickness and 0.125 inch wide wrapped in a closely laid helix about theconductor of diameter 0.178 inch.

The copending application of Elmen Serial No. 473,877, led May 31, 1921,discloses and claims a magnetic material which has properties .adaptingit, among other 'purposes, e to loading signaling conductors inaccordance with this invention.

It.l will normally be found that the high permeabilities referred to inthe foregoing part of this specification are not obtained merely byapplying the loading composition iu the manner described; to obtain thehighest permeability and, consequently, the` greatest inductance, it islnecessary to give the loaded conductor an appropriate heat treatment.For 'this pur ose the conductor specified isdrawn lengt wise through thefurnace of Fig. 3, which is maintained at a temperature of about 87 5'C. This is a muiiie furnace, with the heating elements 1 between thefire clay muiiie 2 and the fire brick 3. Around the fire brick 3 is asheet iron outer wall. The iron tube 4 has a. copper lining 5 lof insidediameter a little over one-half inch. It extends clear across thefurnace and projects 8 inches beyond the furnace walls at each end. .Thelengthy of the pass through the furnace is about 2 feet and' the rate ofmovement of the conf ductor therethrough is about 1%, foot per minute.As the taped conductor passes from the-furnace and the projecting' end,

ofthe tube 4 5, it cools in the air, which duc-tor should be led away'straight from the furnace, farrenough for'it to become cooled; bendingat this stage may impair its high permeability. 4Also the necessaryAcoiling thereafter should be `on a large radius, not less than 2 feet;the strains and stresses involved in 'ceiling and uncoiling on a smallerradius may reduce the permeability. i

While a certain speed and temperatureY vwith a certain type of furnacehave been described to 'pro uce the desired results in the case of aparticular cable, it is apparent vthat these factors may be varied orad]usted to meet diEerent. cases, such, for example,

as a cable of different diameter from that here discussed. In some casesit may be de- Sirable to repeat this heat treatment several times inorder that the strains in the com i position may be completely removedand that the utmost high permeability desiredmay be established therein.Such a repetition of the heat treatment process may be` particularlynecessary in case the conductor is solid instead of being stranded.

Having prepared the bare loaded conductor, an insulating material Vsuchas Chattertons compound is applied in such a manner that all `olftheinterstices of the conductor and the strand are completely filledwith this compound and a layer thereof Aadher'es to the outsideyof thetape and serves to give good adhesion with the gutta perchainsulation,which is applied next. The filling compound should be one which flowsunder a pressure even when cold. A irelatively soft grade of Chattertonscompound has been found suitable fo-r this purpose. The object offilling all the interstices of the conductor with Ghattertons compoundis to provide assurance that when theycable is submerged the pressureapplied to theloading-'tape will not tend to deform' it, as`

might be the 4case if there'were slight voids within the outline of theconductor. Thus it is assured that the great pressure to which thecableis subjected at ocean depths will merely subjectthe loading tape toa` uniformly distributed pressure without distorting it., Thisisdesirablebecause it has been found that the tape of' magnetic materialhas its permeability seriously reduced if it is deformed. i.

The gntta percha insulation is appliedto the loaded conductor in themanner ordinarily employed when insulating submarine cables.

As is the ordinary practice, a long ocean cable must be made up in anumber of sections which will be joined together. If these sectionsdiffer in their characteristic impedance, it will be desirable to jointhem in such a wayfthat these characteristic. im-

pedances are graded consecutively from one section to the next. vIf itis deemed desirable to have the characteristic impedances approximatelythe same at ,the two ends of the cable, this may be accomplishedconsistentl-y with the foregoing requirements by. dividing Ithe cablesections into two groups, each arranged in the order of their impedancesand connected so that the impedances increase gradually. from each endVto the approximate middle of the cable.

Although uniformity of impedance is desirable, particularly-from thestandpoint of balancing with the artificial line incase the cable is tobe operated duplex, nevertheless small variations in impedance fromsection to section are not serious, for the reason c tured.

In order to secure full benei'it of the loading of the type described,certain precautions are .necessary in, connection with operation. lnparticular,`means should be provided for eliminatingor compensatingdistortion so far as possible. Although the heavily loaded cable isdescribed by some authorities as being substantially distortionlessabove'certain signaling speeds, it has been found that actually it givesdistortion at all signaling speeds owing to the alternatingcurrentlosses in the loading material, and it has also been found that it mayintroduce new kinds of distortion which are not present in non-loadedcables. The principal types of distortion to which a loaded cable ofthis type is subject,` are that-diie to unequall attenuation and phaseshift of the' component frequencies of the signal and that due tointroduction of har- .monics as a result of the magnetic peculiaritiesof the loading material. Another type of distortion may be introduced bymagnetic hysteresis in the loading material, but

in the case ofthe magnetic material par ticularly refe'rred'to in thisspecification, it is believed that this kindof distortion will not beserious in view of the very low hysteresis exhibited thereby. v

The distortion due to unequal attenuation and phase shift of thedifferent frequency componentsof the signalis similar to that which isproduced bythe non-loaded cable but -is less in.- degree'. Thisdistortion maybe -reduced by the use of -f proper compensating networkat the terminals of the cable, which will reduce the amplitude of the,com-

ponents of frequencies lower than a certain maximum desired frequency totheir proper value relative. to that of the maximum frequency, that is,itis provided that all'frequencics below the maximum frequency areattenuated alikeby the combination of the cable and the network. Byproper design of the terminal network the necessary restoration ofproper phase relations may also be secured.

A suitable circuit system to complete the cable in accordance with theforegoing principles is illustrated in Fig. 4, where the cable 6 iscontinuously loa-ded in accordance with the disclosure of thisspecification. litis connectedto ground through the transinittingapparatus 7 and. condenser 8. At

the receiving end the cable is connected tov ground through two parallelbranches. One

of these comprises a large inductance 9 in series with an adjustableresistance 10. The other branch comprises the condenser 11 andadjustable resistance 12 in multiple, this combination having seriesrelation to the inductance coil 13`and adjustable resistance 14 inseries with each other. The elements 8, 9, 10, 11, 12, 13 and 14 arecomprised in the distortion-correcting apparatus. The inductance 13 andresistance 14 are shunted by a potentiometer resistance 15, the tapsfrom which complete the 'input grid circuit of the vacuum tube amplifier16, whose output circuit comprises the recording instrument 17. rlhisrecording instrument 17 may conveniently be a string oscillographrecording photographically on sensitized paper. The siphon recorderwhich is commonly used for non-loaded cables'is too slow in operationfor the high speed signals sent over the B5 improved loaded cable ofthis invention.

In placeof the transmitting and recording apparatus which are shown, itmay be advantageous to use the terminal apparatus of the Well-knownmultiplex printing telegraph system in combination with a vibratingrelay of the Gulstad type or of the synchronous type. V

In certain cases advantage may be se- -cured by using the carriercurrent system, in which sinusoidal currents of definite moderatefrequency are modulated -by superposed signal impulses of lowerfrequency. Although the carrier current telegraph system has shownnoadvantage over the standard system for non-loaded cables, it may offeradvantage in the case of continuously loaded cables for the reason thatthe attenuation does not increase so rapidly with the frequency in thecase of the loaded cable as in the case oft/the non-loaded cable.

What is claimed is':

1. A long submarine cable conductor for signals of 'high telegraphicfrequency loadedwith a layer of nickel-iron composition of substantiallyhigher permeability than iron at low magnetizing forces.

2. A long submarine cable conductor for signals of high telegraphicfrequency continuously loaded with a composition coinprising at leasttwo magnetic elements, one of which is nickel, and in which the nickelcomponent is lwithin afew percent of TS1/2% of the magnetic elementcontent.

3. A long submarine telegraplicable conductor enveloped by magneticmaterial coinprising nickel and iron and having a ermeability at leastseveral times that of iron at magnetizingV forces of two-tenths gaiissor less.

4. A long submarine telegraph cable coniprising a uniform conductor anduniformly weeen A graphic frequencies transmitted, the product exceedsthe conductor resistance, all magnitudes being measured inelectromagnetic units.-

5. Along submarine cable comprising a uniform conductor and uniformlydistributed magnetic material comprising nickel and' iron andhaving apermeability at magnetizj.

ing forces of .2 gauss 'orle-ss s uchthat when the permeabilityismultiplied by 2n times a frequency within' the range .of frequenciestransmitted,'the product exceeds the conduc- Weight ofthe alloy.

7. Along-.submarine came' wrapped with sp'irally laid tape of athickness not-exceedi i ing forces of .2 gauss or less.

111g a few milscomposed of an alloy of nickel and iron and a substanceto increase the specific resistance thereof, and having a permeabilitygreater than iron at magnetiz-j 8. A longfsubmarinel cable conductor forI signals of hghtelegraphic frequency loaded with. a layer ofmagneticmaterial comprising .nickel and iron, the nicked content being 7,Within a few per cent of 781/2170 0f the nickeL iron. content; V

i 9. A long submarine telegraph conductor continuously loaded lwithmagnetic material comprising atV least two elements of the magnetic grouandmeans for telegraphing over said con uctor at speeds exceeding 20cycles per second. l

10. A lgng submarine telegraph conductor continnously loaded withmagnetic material 'comprisingat least nickel andriron' ofthe magneticgroup,`and means for telegraphing' over said conductor at speedsexceeding 20 cycles. per second, said material having a permeabilityatleast several times thatof iron at the magnetizing4 forces involved.-

11. A long submarine telegraph conductor loaded with a layer ofmagneticr'niaterial comprising at least two elements-of the magneticgroup, saidmaterialhaving so high' an .initial permeability,l such-highspecificre'- I sistanc'efsuch low hysteresis effect and such Idimensions that the attenuation of telegraph-A ic signals is less thanina non-loaded conductor of the same dimensionsas the com- 1 binedconductor and said layer. Y

12.- A submarineftelegraph conductor continuously' loaded withAmagnetic' material comprising at least two elements of the magneticgroup, said material. having s uch highy permeability, specificresistance, low hystenuation sufl'ered by telegraphic signalstransmitted at a speed between 20 cycl'e'sper second an'dseveral timesthat rate isless teresis eect, and dimensions that the atn l than wouldbe suffered by telegraphic signals of one-half. that speed over anon-loaded conductor of the same outside diameter.

13. A long submarine telegraph -conductor loaded with a layer'ofmagnetic material comprising at least'nickel and iron of the magneticgroup and having a permeabilityy 4' atleast several' times that of ironat, the` magnetizing forces involved, and mea-ns lfor impressmgtelegraplnc signals on-said conductor at high Speed. the attenuation ofsaid' signals in said conductor being less than for an unloadedconductor of thesame dimen- 80 1 sions as the combinedco'nduc'tor andsaid layer.

1.4.- loaded with' a composition comprising nickel and iron, the nickelcontent constituting more than half the total weight of the alloy.

In witness whereof, I hereunto subscribe my name this A long: submarine'cable continuously;

10th day of August A. D.,v t

' f LI'V'ER EfisUcKLEf

